Abstract

The Echinodermata are an ancient phylum of benthic marine invertebrates with a dispersal-stage planktonic larva. These animals have innate immune systems characterized initially by clearance of foreign particles, including microbes, from the body cavity of both larvae and adults, and allograft tissue rejection in adults. Immune responsiveness is mediated by a variety of adult coelomocytes and larval mesenchyme cells. Echinoderm diseases from a range of pathogens can lead to mass die-offs and impact aquaculture, but some individuals can recover. Genome sequences of several echinoderms have identified genes with immune function, including expanded families of Toll-like receptors, NOD-like receptors, and scavenger receptors with cysteine-rich domains, plus signaling pathways and cytokines. The set of transcription factors that regulate proliferation and differentiation of the cellular immune system are conserved and indicate the ancestral origins of hematopoiesis. Both larval and adult echinoderms are in constant contact with potential pathogens in seawater, and they respond to infection by phagocytosis and encapsulation, and employ proteins that function in immune detection and response. Antipathogen responses include activation of the SpTransformer genes, a complement system, and the production of many types of antimicrobial peptides. Echinoderms have homologues of the recombinase activating genes plus all associated genes that function in vertebrates for immunoglobulin gene family rearrangement, although their gene targets are unknown. The echinoderm immune system has been characterized as unexpectedly complex, robust, and flexible. Many echinoderms have very long life-spans that correlate with an excellent capacity for cell damage repair. In many marine ecosystems, echinoderms are keystone predators and herbivores, and therefore are species that can serve as optimal sentinels of environmental health. Coelomocytes can be employed in sensor systems to test for the presence of marine pollutants. When Elie Metchnikoff inserted a rose prickle into a larval sea star and observed chemotaxis, phagocytosis, and encapsulation by the mesenchyme cells, he initiated not only the field of immunology but also that of comparative immunology, of which the echinoderms have been an important part.

Notes

Dedication

This work is dedicated to Valeria Matranga who passed away too young in April 2016 after a long and courageous battle against cancer. Valeria contributed immensely to our understanding of cellular and molecular immune processes in the sea urchin, Paracentrotus lividus. Her dedicated research on echinoderms led to an understanding of how they interact with their environment and how coelomocytes can be employed to evaluate environmental toxins and pollutants. She and her insight for creative approaches in eco-immuno-toxicology will be missed because her approach to thinking about how to answer difficult scientific questions would have been more and more valuable in the future.

AcknowledgementsResearch by the authors that was the basis of some of the information integrated into this chapter was supported by funding from the US National Science Foundation to LCS, DAR, MO, and JHH; the National Institute on Aging, a Bermuda charitable trust, and The Christian Humann Foundation to AGB; the European Molecular Biology Organization to NF; the Keio Gijuku Academic Development Funds to RF; the Chang Gung Medical Research Program and the Ministry of Science and Technology to SDF; HORIZON 2020 – The EU Framework Programme for Research and Innovation under the Marie Skłodowska-Curie Actions to AP; the Australian Research Council to DAR; the Canadian Institutes for Health Research and the Natural Sciences and Engineering Research Council of Canada to JPR; and the Tromsø Forskninsgstiftelse and the UiT The Arctic University of Norway to KS.

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